Lung epithelium is critical to normal gas exchange and maintenance of a physical and immu- nologic barrier against environmental dangers. Acute loss of epithelium can have devastating consequences, including loss of gas exchange, surfactant synthesis, airway obstruction, and increased susceptibility to secondary infections. The processes that regulate epithelial cell sur- vival are critical to how lung epithelium responds to acute and chronic environmental challenges with important consequences for lung function and host survival. We have identified new path- ways by which hyperthermia, such as occurs in fever, clinical hyperthermia syndromes and en- vironmental exposures, accelerate apoptosis in lung epithelium and worsen lung injury. The overall objective of this application is to elucidate the mechanisms by which hyperthermia within the febrile range modifies lung epithelial injury and recovery. Our central hypothesis is that ex- posure to hyperthermia concurrent with activation of death receptors (e.g. TNF Receptor- 1/TNFR1 or fas) accelerates assembly of the death inducing signaling complexes, augments downstream pro-apoptotic pathways, and inhibits anti-apoptotic factors. The rationale for our hypothesis is based on our recent studies demonstrating that (1) co-exposure to hyperthermia in the HS (42C) or febrile (39.5C) range greatly increases and accelerates caspase-3 activation and apoptosis in mouse MLE15 lung epithelial cells after TNF treatment or fas activation and is independent of NFB and the major heat activated transcription factor, HSF-1, and (2) there is a limited time window following TNF treatment but not fas activation after which cells are pro- tected from HS-augmented apoptosis (discussed in the Preliminary Data section). We will utilize MLE-15 mouse lung epithelial cells, BEAS2B human lung epithelial cells, and primary cultured human small airway epithelial cells (SAECs), and an in vivo intratracheal LPS-induced mouse ALI model to pursue the following specific aims: (1) determine how hyperthermia alters TNF- and fas-activated death-inducing signaling complexes, their composition, and function and the consequences for cell survival vs. death; (2) delineate the effect of hyperthermia on JNK MAP kinase signaling and the consequences for cells survival vs. death in cells TNF-treated cells; (3) analyze the mechanisms of hyperthermia-enhanced apoptosis in human lung epithelial cells, and (4) analyze the contribution of accelerated epithelial apoptosis to LPS-induced lung injury. We expect that the results of the proposed studies will identify new pathophysiologic pathways that contribute to lung injury under clinically relevant conditions. The pharmacologic studies in aim 4 will provide new preclinical data that may lead to future therapies in patients with ALI.